Process for producing nodular iron



United States Patent 3,362,814 PROCESS FOR PRODUCING NODULAR IRON John C. Robertson, Midland, Mich, and Oliver Osborn, Lake Jackson, Tex., assignors to The Dow Chemical Company, Midland, MiClL, a corporation of Delaware No Drawing. Filed Feb. 23, 1965, Ser. No. 434,633 2 Claims. (Cl. 75-130) ABSTRACT OF THE DISCLGSURE A process for treating ferrous based melts, particularly for producing nodular grey cast iron, which comprises introducing predetermined quantities of scandium into a ferrous based melt and maintaining this material therein for a predetermined period of time.

This invention relates to the treatment of molten ferrous based maten'als and more particularly is concerned with a novel process for preparing ductile, i.e. nodular grey cast iron.

It is known in the art that certain metals, magnesium being most commonly employed, which are retained in cast iron in amounts over and above that required for desulfurization will cause uncombined carbon present therein to be present in a compacted form and preferably a spheroidal form. Such cast iron, known as nodular iron, is ductile and possesses properties different from and improved over that found is grey cast iron where the uncombined carbon is present as the normal flake graphite. The terms nodular iron and nodularization as used hereinafter referred to iron having spheroidal, i.e. compacted graphite inclusions, and to the process by which these are formed.

A wide variety of processes and apparatus relating to the introduction of these metals, and magnesium in particular, into molten cast iron are in the known art. These known techniques usually employ either complicated processing equipment and/ or use alloys or other compositions whereby undesirable substances are introduced into the molten ferrous melt along with the magnesium. Usually violent, uncontrolled, hazardous reactions accompany the introduction of magnesium into the melt in the employment of a majority of such known processes. Now, unexpectedly, we have discovered a safe, simple improved process for preparing nodular iron.

It is a principal object of the present invention to provide a novel process for making ductile iron whereby a rapid but nonviolent treatment is realized with substan tially complete nodularization of the graphite in the iron product along with the establishment of a desirable high residual content of the treating agent in the iron product.

It is a further object of the present invention to provide a process suitable for use in nodularizing iron which obviates the need for special plunging equipment to introduce a treating agent under the bath surface and requires no complicated mechanical application equipment.

It is another object of the present invention to provide a nodularizing agent and process which are safe to use and operate and which obviate the need for covered ladles or other special pressure resistant equipment as are employed in many conventional nodularizing processes.

It is an additional object of the present invention to provide a process for treating molten cast iron that does not introduce into the melt undesirable constituents which may alloy therewith.

It is still another object of the present invention to provide a process for nodularizing cast iron in which there is less fadding, i.e. loss, of the treating agent from the ice melt, than from magnesium thereby permitting longer ladle holding times.

It is a further object of the present invention to provide a process for nodularizing iron wherein alloying elements commonly employed as a carrier with magnesium, are not introduced into the melt as results in many conventional nodularizing processes. This instant invention thereby permits (1) the incorporation of large quantities, 70 percent or more, of gates, risers, rejects and other scrap into subsequent remelts without adversely affecting the properties of the iron or overshooting elemental specification in the finished iron, and (2) the use of a heavier post inoculation treatment which is particularly desirable for thin sectional castings.

It is also an object of the present invention to provide a process for nodularizing iron melts wherein there is substantially no loss of the ferrous-based melt because of spillage, splattering or other violent reactions during the treatment and which is not accompanied by undesirable blinding light, pyrotechnics and burning and noxious fumes.

These and other objects and advantages will become apparent from the detailed description presented hereinafter.

In accordance with the present invention, substantially complete nodularization of graphite and retention of a desirably high concentration of treating agent in cast iron is obtained by introducing scandium into a molten iron bath.

The amount of scandium to be employed in treating a molten mass of a ferrous based material, e.g. grey iron, by the instant process, ranges from about 0.25 to about 10 pounds or more scandium per ton of the ferrous based metal. Ordinarily, scandium is added in a concentration of from about 1 to about 5 pounds of scandium per ton of molten cast iron.

In carrying out the instant process, scandium in a predetermined amount within the range set forth hereinbefore, is introduced as by a plunger bell, for example, into a ferrous based melt, e.g. a molten grey iron bath. The so-treated melt is maintained in the molten state for a period of from about 0.1 to about 20 minutes, ordinarily from about 0.25 to about 8 minutes and preferably from about 0.25 to about 2.5 minutes. Following this reaction period, the molten iron ordinarily is given as conventional post-inoculant treatment, as by introducing ferrosilicon therein. The resultant melt upon casting, cooling and solidifying provides ductile cast iron products wherein substantially all of the graphite is in a compacted, spheroidal form.

Particulated scandium usually is employed in the process of the present invention. The size or shape of this nodularizing agent is not critical except that the particles must not be of such a massive size that they provide a high mass to surface area relationship such that dissolution and reaction in the molten ferrous melt is detrimentally retarded. Powders, pellets, flakes, machine chips, curled cuttings, filings, sawdust, chopped foil and the like particles either alone or in the form of compacts have been found to be particularly effective forms of scandium for use in the present process. It is not necessary to use a high purity scandium metal.

The scandium can be introduced into a ferrous melt by simply adding it thereto with agitation or by other conventional means as known to one skilled in the art. A perforated graphite plunging bell is a convenient means for use in getting the scandium into the melt. With this device, the scandium readily becomes homogeneously dispersed throughout the melt as it dissolves after introduction under the surface of the melt. Preferably the scandium is added near the bottom of the melt to take advantage of natural convection and conduction currents in the melt which aid in the homogeneous distribution of the agent throughout the melt.

In the present process the scandium can be introduced into a melt maintained at any temperature at which the ferrous mass is in the molten state. A marked advantage of the process of the present invention is that there is a marked reduction in scandium losses from vapor loss during processing over that realized with processes using magnesium as a nodularizing agent. This gives the further advantage that simpler equipment and techniques of addition can be employed for the present nodularizing agent.

The nodular iron products resulting from the present process can be used in any application and/or subsequently processed by any of the techniques employed for ductile iron.

The following example will serve to illustrate further the present invention, but is not meant to limit it thereto.

Example.An induction furnace having a capacity of about 4 pounds of molten iron and equipped with a tilting mechanism was charged with a grey iron having the following composition:

Element: Weight percent Carbon 3 .3 7 Manganese 0.31 Silicon 1.30 Phosphorus 0.03 Sulfur 0.004 Iron Balance About 3.8 pounds of cast iron was placed in the furnace and power of about 6 kilowatts was applied thereto to melt the charge. The temperature of the resulting melt was maintained at about 2750 F. At this melt temperature, about 2.06 grams of scandium metal in the form of a small chunk (equivalent to 2.1 pounds scandium per ton of cast iron) was introduced under the surface of the melt by means of a perforated graphite plunger bell. Within about 10 seconds, the scandium smoothly and quietly dissolved in the melt. There were no visible signs of any violent turbulence, flaring, fuming; or pyrotechnic display of any type. The plunger then was withdrawn from the melt, the total time of immersion being about seconds, and about 32 grams of an 85% ferrosilicon was rabbled into the melt following conventional graphitizing post-inoculant procedures. The so-treated iron was cast into a standard ASTM /2 inch Y-block shell mold backed with sand. Standard inch diameter ASTM tensile test specimens were cut from the resulting Y-block casting in accordance with ASTM procedure A-445-60T.

Analysis of machine turnings from the cast specimen by emission spectroscopy showed a residual scandium content of 0.026 weight percent. Microscopic examination of the casting indicated that the graphite was substantially all in the desired compacted, nodular form.

In a manner similar to that described for the foregoing example, chips, pellets, compacted briquets of powdered scandium, and the like can be stirred into, introduced under the surface of or otherwise incorporated into a terrous based cast iron melt in an amount of from about 0.25 to about 10 pounds scandium per ton of melt and preferably from about 1 to about 5 pounds scandium per ton of melt in accordance with the present novel process thereb yto efiect nodularization of the graphite contained therein.

Various modifications can be made in the present invention without departing from the spirit or scope thereof for it is understood that we limit ourselves only as defined in the appended claims.

We claim:

1. A process for producing grey cast iron containing spheroidal graphite and scandium which comprises;

(a) introducing into a molten mass of grey cast iron from about 0.25 pound to about 10 pounds scandium per ton of said ferrous based metal,

(b) maintaining said scandium in said molten mass for a period of time ranging from about 0.1 to about 20 minutes, and

(c) casting the scandium-treated molten grey iron thereby to prepare cast grey iron containing spheroidal graphite and scandium.

2. A process for producing grey cast iron containing spheroidal graphite and scandium which comprises;

(a) introducing into a molten mass of grey cast iron scandium metal in an amount equivalent to about 2 pounds of scandium per ton of said grey cast iron,

(b) maintaining said scandium metal in said molten mass for about 0.25 minute, and

(c) casting the scandium-treated molten grey iron thereby to prepare cast grey iron containing spheroidal graphite and scandium.

References Cited UNITED STATES PATENTS 3,055,756 9/1962 Kanter -130 X 3,146,090 8/1964 Kanter 7513O X OTHER REFERENCES HellaWellLetter in J. Less-Common Metals; February 1962; vol. 4; pp. 101-103.

GeiselmanArticle in J. Less-Common Metals; August 1962; vol. 4; pp. 362, 375.

DAVID L. RECK, Primary Examiner.

H. W. TARRING, Assistant Examiner. 

